1. Field of the Invention
This invention relates to a chip resistor wherein a film-like resistor element is formed on an electrically insulating substrate chip. The present invention also relates to a method of making chip resistors.
2. Description of the Prior Art
The applicant has formerly invented such a chip resistor as disclosed in Japanese Patent Application Laid-open No. 4-102302. For convenience of explanation, the configuration of this known chip resistor is illustrated in FIGS. 12a-12c.
As shown in FIGS. 12a-12c, the prior art chip resistor, generally designated by reference numeral 30, comprises an insulating substrate chip 31 made of e.g. ceramic. A film-like resistor element 33 covered by a glass coating 32 is formed on the chip 31 in conduction with a spaced pair of main electrodes 34. An auxiliary electrode 35 is formed on each of the main electrodes 34, and an end electrode 36 is formed on each end face of the chip 31 in conduction with the corresponding main and auxiliary electrodes 34, 35. Further, the auxiliary and end electrodes 35, 36 are covered by an unillustrated plating of e.g. nickel.
According to the prior art, the auxiliary electrode 35 reduces the degree of level difference from the coating 32, thereby increasing the surface flatness of the chip resistor 30 as a whole. Thus, a vacuum collet A (FIG. 12a) of an automatic mounting apparatus can still be used for conveniently picking up the chip resistor 30 to mount it onto a circuit board even if the chip resistor 30 comes positionally out of alignment with the collet A.
Further, the increased surface flatness of the resistor chip 30 is also significant in properly mounting the chip 30 on a circuit board B (including a circuit B1) in an inverted state because both of the auxiliary electrodes 35 can be reliably brought into contact with corresponding solder deposits C, as shown in FIG. 12b. If, on the other hand, no auxiliary electrode is provided, the resistor chip tends to be unstable so that it is more likely to be mounted improperly (tilted), as shown in FIG. 12c.
However, the prior art resistor chip described above still has the following problems.
In an automatic chip mounting apparatus, use is made of a flexible supply tube D which is made of a synthetic resin for example and has a rectangular cross section, as shown in FIG. 12a. The resistor chip 30 is loaded into the tube D for transfer and taken out from the tube D at the site of chip mounting for picking up by the vacuum collet A.
According to the prior art arrangement, since each auxiliary electrode 35 extends over the full width of the substrate chip 31, the sharp edges of the electrode 35 tends to be easily caught within the tube D, consequently hindering smooth supply of the chip resistor 30. Particularly, when the auxiliary electrode 35 is covered by a metallic plating (e.g. nickel plating), the plating will have burrs at the edges of the auxiliary electrode 35, thereby increasing the possibility of the chip resistor 30 being caught in the tube D.